Long Term Evolution (LTE) communication systems supply User Equipment (UE) with wireless access to communication services, such as Internet access and Voice over LTE (VoLTE) calling. The LTE systems include Packet Gateways (P-GWs) that interface with external systems, such as the Internet and an Internet Multimedia Subsystem (IMS). The LTE systems also include Policy, Charging, and Rules Functions (PCRFs) to control Quality-of-Service (QoS) and bandwidth allocations at the P-GWs. The P-GWs and PCRFs interact to establish media bearers between UEs and P-GWs. The P-GWs and PCRFs also interact to establish IMS bearers between UEs and IMS servers.
To place a VoLTE call, a UE exchanges Session Initiation Protocol (SIP) messages with an IMS Proxy Call Session Control Function (P-CSCF) over its IMS bearer. In response, the IMS CSCF systems exchange SIP messages with other systems to establish the voice session. If the voice session is accepted, the P-CSCF instructs the LTE PCRF to add a voice bearer for the VoLTE call. In response, the LTE PCRF supplements the voice bearer instruction with QoS and bandwidth allocation data and forwards the supplemented voice bearer instruction to the LTE P-GW. The LTE P-GW then establishes the voice bearer, and the P-CSCF transfers a SIP message to the UE over the IMS bearer to use the voice bearer for the VoLTE call. The UE then exchanges voice packets with the LTE P-GW over the voice bearer, and the P-GW exchanges the voice packets with the other systems to extend the voice path for the call.
A key aspect of this VoLTE process is the IMS P-CSCF instruction to the LTE PCRF to add the voice bearer for the call. The LTE PCRF supplements the voice bearer instruction with QoS and bandwidth data, and transfers the supplemented voice bearer instruction to the LTE P-GW. If the LTE PCRF is not available due to an outage, then the P-CSCF may provide an alarm or notice, but the media session may not occur. Current techniques to handle PCRF outages on VoLTE sessions are not efficient and effective.